Emissions and effluents from industrial processes often require the removal or neutralization of offensive substances before they can be discharged into the environment. One such emission is that from a fluid catalytic cracker regenerator, which emission requires the removal of sulfur. The sulfur from the gaseous emission is generally removed by wet gas scrubbing. The gases sent into the air are freed of sulfur, but the effluent scrubber stream, however, requires neutralization of the sulfuric acid formed by the absorbed sulfur.
Also, in processes requiring a sulfite oxidation reactor basin, the acidic effluent from the basin must be carefully neutralized before it can be discharged into the environment.
In waste water treatment caustic, and/or acid is often added to effluent streams to neutralize them (control pH) before they are allowed to exit to the environment.
In cooling tower operation, it is important to control pH in order to minimize the risk of foulant formation.
The present invention is concerned with the neutralization, or otherwise control of the pH, of effluent process streams.
In the past, it has been known to construct large backmixing facilities to capture the process stream and to allow for the thorough mixing thereof, in order to properly analyze and treat the effluent. Backmixing facilities were used in order to provide needed stable control of the pH. Without them, pH due to its highly non-linear behavior, could not be automatically controlled. Backmixing vessels also provide the side benefit of thorough mixing of the effluent stream needed to avoid large variations in effluent pH. These facilities were expensive to construct, and often required many hours to add and thoroughly mix a neutralizing reagent into the captured effluent.
In the case of a sulfite oxidation reactor basin, there is often a holdup time of twenty hours. While in the reactor basin the oxidation reaction is continuously proceeding and byproducts are continuously formed which modify the reagent addition requirements for reaching neutralization. Therefore, the amount of reagent required to neutralize the stream cannot be known without completion of the oxidation reaction. With the prior art system, it could not be known for twenty hours whether the proper amount of neutralizing reagent had been added (a hit or miss proposition). Moreover, modification of the reagent addition rate based upon the current basin outflow pH would not result in proper neutralization of subsequent effluent due to continuous changes in the effluent composition. The invention provides a means of continuous reagent additions to insure continuous neutralization at the basin outflow.
To the best of our knowledge and belief, in a process stream having low buffering (highly logarithimic reagent reaction characteristic) no one has successfully added neutralizing reagents on a continuous basis to a flowing process stream without the use of a backmixing vessel. This is so, because the logarithmic definition of pH, imposes stringent requirements on the pH control system's resolution, rangeability and dynamic response. In other words, the non-linearity of the neutralization process requires a control response which cannot keep pace with the instantaneous pH readings.
From a pH control standpoint, the use of a large backmixing facility reduces the dynamic gain of the system, such that neutralization can be more easily achieved.
The present invention has as one of its objectives to control the pH of a process stream on a continuous basis, while eliminating the need for costly backmixing facilities.
The present invention also seeks to provide a system and method for controlling the pH of a process stream in a quick, efficient manner.
The present invention achieves the stability of effluent stream composition by replacing the process stream backmixer with the far less costly sample stream mixer.
These and other objects of this invention will be better understood and will become more apparent with reference to the following detailed description considered in conjunction with the accompanying drawings.